560 



Plague 



Both insects hop about in search of the appropriate warm-blooded hosts upon 

 whose blood they are to live. Each kind of flea has a preferred host, but the 

 tastes of all are more or less cosmopolitan, so that in the absence of the preferred 

 host, another kind of warm-blooded creature will do. Adult fleas live solely by 

 sucking blood. 



The longevity of a flea varies according to conditions of temperature and mois- 

 ture Life is longest when the temperature is high and the ground not too dry. 

 They may live for months without feeding; when regularly fed they can live at 

 least a year and a half. The longevity of the fleas in the adult stage, the long 

 periods of abstention from food that they may suffer without dying, and the ac- 

 cessions to their numbers that may occur through the perfection of their embry- 

 onal fellows in the same place, explain why families returning to their closed city 

 houses, or going to their closed country houses, sometimes find them after months 

 of desertion, occupied by a welcoming host of fleas. They are the progeny of 



r 



MiTOSrs 

 /MJ^n 



c ^ 



Fig. 231. Various fleas, magnified about 30 diameters. The specimens are 

 treated with hot 20 per cent, caustic potash for a few minutes, dehydrated in 

 alcohol, cleared in xylol and mounted in balsam, a, Ceratophyllus fasciatus d"; 

 b, Ceratophyllus fasciatus, 9 \c , Leptopsylla musculi, cf ; d, Leptopsylla musculi, 9 

 (Bacot, in Journal of Hygiene, "Plague Supplement in, 1914"). 



the fleas of the former dog, cat, rat or mouse tenants, that have matured or 

 survived the interval and are now hungry because the removal of the family 

 months before, was probably followed by the withdrawal of the rats and mice no 

 longer able to find food in the deserted habitation. 



To get rid of such fleas is often a perplexing question. A way to accomplish 

 it is to place a cage containing a cat or a guinea-pig, or a trap containing living 

 rats or mice on the floor of a room and surround it by sticky fly-paper. Fleas 

 when empty and hungry, were found by Strickland* to be able to jump 4 inches; 

 those recently fed only 3 inches. In their endeavors to reach the caged animals 

 the fleas jump upon the fly-paper and are caught. This can be done in several 

 rooms of the house and soon cleans up the fleas. 



During such periods of fasting the sexes do not copulate and no ova are pro- 

 duced^ As soon as blood is taken, copulation takes place, and if the blood be 



* "Journal of Hygiene," 1914, xiv, p. 129. 



